Gypsum vs. Anhydrite: What's the Difference?
Edited by Aimie Carlson || By Harlon Moss || Published on November 23, 2023
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, whereas anhydrite is its anhydrous form, lacking water in its structure.
Key Differences
Gypsum, a widely used mineral, is known for its softness and is composed of calcium sulfate dihydrate. Anhydrite, on the other hand, is a hard mineral, the anhydrous form of calcium sulfate, and is often found in salt deposits.
In terms of usage, gypsum is a key ingredient in plaster and drywall, owing to its bonding properties and ease of shaping. Anhydrite, due to its hardness and lack of water, is less versatile in construction but is valuable in the manufacture of certain cements.
Gypsum can easily be converted to anhydrite by heating, a process that removes water. Conversely, anhydrite can absorb water to convert back into gypsum, a property used in some industrial processes.
The occurrence of gypsum is often in sedimentary rock formations and can be mined in large quantities. Anhydrite is also found in sedimentary basins but is less common and usually deeper underground.
Both minerals are essential in geological studies for understanding sedimentary environments, with gypsum indicating a more watery past environment compared to the drier conditions indicated by anhydrite.
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Comparison Chart
Chemical Composition
Calcium sulfate dihydrate (CaSO4·2H2O)
Calcium sulfate anhydrous (CaSO4)
Hardness
Soft, can be scratched with a fingernail
Harder than gypsum
Usage in Industry
Used in plaster, drywall, and as a fertilizer
Used in cement and as a drying agent
Water Content
Contains water molecules in its structure
Lacks water in its crystal structure
Formation Conditions
Forms in watery environments
Indicates drier sedimentary conditions
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Gypsum and Anhydrite Definitions
Gypsum
Used in sculpture and art for casting molds.
Artists often use gypsum to create detailed molds.
Anhydrite
A hard mineral consisting of anhydrous calcium sulfate.
Anhydrite deposits were found beneath the salt dome.
Gypsum
A mineral used as a fertilizer for its high sulfur and calcium content.
Gypsum was added to the soil to improve its quality.
Anhydrite
Anhydrite can transform into gypsum when exposed to water.
Over time, the anhydrite absorbed moisture and became gypsum.
Gypsum
A soft white or gray mineral used in making plaster.
The walls were made of gypsum plaster.
Anhydrite
Used as a drying agent due to its moisture-absorbing properties.
Anhydrite was used to dry out the damp soil.
Gypsum
Gypsum is found in sedimentary rock formations.
The geologist discovered gypsum layers in the rock strata.
Anhydrite
Used in the manufacture of certain types of cement.
The factory utilized anhydrite as a cement additive.
Gypsum
Gypsum boards are used in construction for drywall.
The contractor used gypsum boards for the interior walls.
Anhydrite
Found in salt domes and sedimentary basins.
Anhydrite layers indicated a dry period in the region's geological history.
Gypsum
A widespread colorless, white, or yellowish mineral, CaSO4·2H2O, used in the manufacture of plaster of Paris, various plaster products, and fertilizers.
Anhydrite
A colorless, white, gray, blue, or lilac mineral of anhydrous calcium sulfate, CaSO4, occurring as layers in gypsum deposits.
Gypsum
A mineral consisting of hydrated calcium sulphate. When calcinated, it forms plaster of Paris.
Anhydrite
(mineral) An evaporite mineral made of anhydrous calcium sulfate.
Gypsum
A mineral consisting of the hydrous sulphate of lime (calcium). When calcined, it forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.
Anhydrite
A mineral of a white or a slightly bluish color, usually massive. It is anhydrous sulphate of lime, and differs from gypsum in not containing water (whence the name).
Gypsum
A common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)
FAQs
What is anhydrite's main chemical composition?
Anhydrite is composed of anhydrous calcium sulfate.
Is gypsum soft or hard?
Gypsum is quite soft and can be scratched with a fingernail.
How is gypsum important in agriculture?
It's used as a soil amendment for its sulfur and calcium content.
Does gypsum contain water in its structure?
Yes, gypsum contains water molecules in its structure.
Is anhydrite used as a drying agent?
Yes, its moisture-absorbing properties make it a good drying agent.
What is gypsum primarily used for?
Gypsum is used in making plaster, drywall, and as a fertilizer.
Can anhydrite be used in construction?
Anhydrite is less common in construction, often used in cement.
Can gypsum be converted to anhydrite?
Yes, by heating and removing water, gypsum becomes anhydrite.
What indicates the presence of gypsum in sedimentary rocks?
Layers of gypsum in rocks indicate past watery environments.
Does anhydrite have any industrial applications?
It's used in cement manufacture and as a drying agent.
Where is anhydrite typically found?
Anhydrite is found in salt domes and deep sedimentary basins.
Is anhydrite harder than gypsum?
Yes, anhydrite is harder than gypsum.
How is gypsum used in art?
It's used in sculpture and casting molds.
What color is gypsum?
Gypsum is typically white or gray.
Can gypsum be used in drywall production?
Yes, it's a primary material in drywall.
Can anhydrite transform into gypsum?
Yes, anhydrite can become gypsum when exposed to water.
What geological information does anhydrite provide?
It indicates drier sedimentary conditions in the past.
Are gypsum and anhydrite found together?
They can be found in similar environments but indicate different conditions.
Is anhydrite soluble in water?
It's less soluble than gypsum but can absorb water.
Is gypsum a common mineral?
Yes, it's a common and widely mined mineral.
About Author
Written by
Harlon MossHarlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie CarlsonAimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.
